This invention relates to semiconductor wafer processing and, particularly, to preparing singulated semiconductor integrated circuit die.
At some stage in die preparation, the wafer is cut to singulate the die. That is, the wafer is cut (for example, by sawing the wafer along “streets” between active circuit regions of the die), forming an array of die (a “wafer array”) on the wafer support. The singulated die can then be manipulated individually (for example by use of a “pick-and-place” tool) for further treatment.
Many die preparation procedures can be carried out at the wafer level, that is, prior to die singulation. However, some procedures for preparing die require access to die sidewalls. For example, it may be necessary to provide electrical insulation over the die edge and sidewalls, to prevent shorting of the semiconductor body of the die with electrical conductors that may be employed for interconnection of the die, and that may contact the die edge or die sidewall.
Such procedures can be carried out on individual singulated die. However, for increased throughput it can be advantageous to carry out such procedures on the die prior to removing the die from the wafer array.
Typically, singulated die may shift on the support. Singulated die may rotate, for example, or may move in relation to the array and, as a result, the shifted die are no longer in proper register. In particular, movement of the dicing saw during the wafer cutting procedure may cause die to shift out of register.
Out-of-register die can present challenges for subsequent preparation of the die in the array.
For example, die shift may result in a narrowing of the spaces between the die in the array, so that the streets are narrowed at some places, or are not straight. Where a subsequent die preparation procedure calls for an additional pass of a cutting tool through the street, the tool may impact and damage shifted die during the additional pass. For example, it may be desirable to apply a die attach film to the backside of the die array, and then to cut the die attach film by passing a cutting tool through the streets in the array, resulting in an array of individual film-backed singulated die.
And, for example, die shift may result in displacement of features on the die out of register. Where a subsequent die preparation procedure calls for treatment of these features, the displaced features may be no longer accessible to equipment for carrying out the subsequent procedure. Shift of the features out of register may cause failure of such procedures. For example, it may be desirable using a patterned mask or stencil or an automated tool to address the interconnect pads on the die to apply an interconnect terminal, for example, or to remove a passivation layer that overlies the pads.
Die shift can in such instances frustrate an effort to increase throughput, by resulting in damaged die or in unsuccessful procedures.